1. Field of the Invention
The present invention relates to an engine waste heat recovering apparatus, and particularly to an apparatus recovering waste heat generated from an engine used as a power source in a cogeneration system.
2. Description of the Related Art
As environmental protection has been a global major issue, cogeneration systems having a gas engine as a power source fueled with city gases for both the generation of electric power and the supply of hot water are now focused to efficiently recover heat generated by the operation of the engine. One type of such cogeneration system is provided with an exhaust gas heat exchanger for recovering heat from the exhaust gas of the engine.
The exhaust gas heat exchanger includes a means for discharging condensed water generated during the cooling down of the exhaust gas. For example, a scheme disclosed in Japanese Patent Laid-open Publication (Heisei) 11-72018 permits the condensed water to be discharged from a drain passage with a waste water trap mounted in the bottom of a muffler.
That type of the cogeneration system enables the recovery of heat at high efficiency and can thus be used particularly in cold districts. In a cold district, the condensed water may be frozen in the waste water trap during the cold season or in early morning or late night in winter. For avoiding such freezing of the condensed water, the drain passage is commonly heated by an electric heater. However, if there is little room for installation of the electric heater, a limited size of the electric heater can only be used. Also, the use of an electric heater may increase the consumption of electric power.
The present invention has been developed in view of the above aspects and its object is to provide an engine waste heat recovering apparatus capable of inhibiting the freezing of condensed water without using an extra component such as an electric heater requiring a considerable size of room and without increasing the consumption of power.
As a first feature of the present invention, an engine waste heat recovering apparatus having an exhaust gas heat exchanger for recovering heat from the exhaust gas of an engine and a drain passage for discharging the condensed water generated by heat exchange in the exhaust gas heat exchanger, comprising, a joint for communicating an internal heat transfer medium path with an external heat exchanger externally installed from the waste heat recovering apparatus, a water pump for circulating the heat transfer medium in the heat transfer medium path, a waste water trap provided across the drain passage, the waste water trap being extended across the joint to the outside; and a defrosting means for switching the water pump on when condensed water is frozen in the waste water trap.
As a second feature of the present invention, the engine waste heat recovering apparatus, further comprising a silencer for separating the condensed water from the exhaust gas released from the exhaust gas heat exchanger, wherein the joint has a passage provided therein for receiving the exhaust gas from the exhaust gas heat exchanger and transferring it to the silencer and the condensed water separated in the silencer is conveyed to the waste water trap.
As a third feature of the present invention, the engine waste heat recovering apparatus, further comprising, a sensor for detecting the temperature of at least one of the waste water trap and waste water, and a freeze detecting means for comparing the temperature detected by the sensor with a reference temperature representing the frozen state of the waste water in the waste water trap, wherein, when it is judged that the waste water trap is in a frozen state on the basis of a result of the comparison, the water pump is switched on.
As a fourth feature of the present invention the sensor is mounted to the joint.
According to the first to fourth features of the present invention, when the condensed water is in a frozen or near frozen state (phase) in the waste water trap, the water pump is switched on for circulating the heat transfer medium. As the heat transfer medium is circulated through a heat exchanger externally or separately installed from the waste heat recovering apparatus, its temperature is as high as a degree of the temperature of the heat exchanger or, more particularly, the temperature of hot water in the hot water storage tank in which the heat exchanger is equipped. As the waste water trap is provided in a joint communicated with the circulating path of the heat transfer medium, the frozen or near frozen state of its condensed water can be eliminated by thermal energy of the heat transfer medium.